Injectors for regular use by the patient, such as for example pen injectors and automatic injectors, should preferably be provided with means for covering the needle when the injector is not used to prevent any needle stick injuries. This can for example be done by means of a cap which can be slid onto the injector housing. Often, the needle is kept sterile in a rigid needle shield (RNS) or a flexible needle shield (FNS), which is also covered by the cap. In order to avoid damage to the needle upon retraction of the cap, it is important to avoid any relative rotational movement between the needle shield and the needle. One solution to this problem is to provide the cap and the injector housing with connecting means which prevents a user from rotating the cap during retraction thereof. By doing so, retraction of the cap can only be done by an axial movement of the cap, thus avoiding relative rotational movement between the needle shield and the needle. This has a major drawback in that it can be very hard for some users, e.g. impaired or elderly, to retract the cap with an axial movement.
WO-2009/040601 describes a method where rotational movement of the cap relative to the housing is translated into an axial movement of the cap by helical means. To avoid relative rotational movement between the needle shield and the needle, the needle shield is fixedly mounted within a sheath which in turn is mounted to the cap such that it may rotate relative the cap. Thereby the rotational/axial movement of the cap is translated into an axial movement only of the needle shield.